Now that you have shown the photo where it indicates that your DR may be off face (left side gas escaping) and also that the trigger in question is the left side trigger, the issue with increasing pressure needed to pull the left trigger may likely be unrelated to the contact between the sear and the tumbler of the left side of the action. With your photo showing a problem on the left side the first thing I would check if I had this DR in my shop is contact of butt stock wood to the left sear.
In regard to the concern about the gas escaping from the left chamber and the DR may not be off face. I see two things from the photos. 1) there is no imprint of the cartridge rim on the left face of the action and 2) the rim depth of the chamber seems too deep. If the left chamber was reamed improperly then you have a significant problem.
JJ Perodeau is renown for his double rifle work.
I see that you are in Michigan and currently I cannot think of a double rifle gunsmith there, but I suggest that you telephone Brian Bilinski owner of Field Sports in Traverse City and ask him if he knows of such a double rifle and trigger expert gunsmith in Michigan.
Kindest Regards;
Stephen Howell
Last edited by bushveld; 09/23/23 12:00 PM.
